Magnetic stirrer



May 21, 1968 L. R. WORTH MAGNETIC STIRRER Filed May 31, 1967 INVENTOR.

FIG. 3.

LOW HIGH 7 MED.

FIG.

United States Patent 3,384,353 MAGNETIC STIRRER Lewis R. Worth,Deerfield, Ill., assignor to Cole-Farmer Instrument & Equipment Company,Chicago, 111., a corporation of Illinois Filed May 31, 1967, Ser. No.643,317 7 Claims. (Cl. 259-108) ABSTRACT OF THE DISCLOSURE A magneticstirrer is described in which a compound magnet comprised of two magnetstructures is utilized. Means are provided for supporting a liquidcontainer having a stirring element formed of magnetic material thereinwithin the field established by at least one of the magnet structures ofthe compound magnet. The rotation of the compound magnet causes aconcurrent rotation of the stirring element within the liquid in thecontainer.

This invention relates to magnetic stirrers and, more particularly, toan improved magnetic stirrer which is capable of utilization inconnection with [a wide range of sizes of stirring elements or bars attheir maximum efliciency without sliding, drifting or jumping.

Magnetic stirrers are used to agitate fluid in a container or vessel ina manner which facilitates access to and visibility of the fluid in thecontainer. No agitator shafts or other devices extend into the containerwhen used with a magnetic stirrer, thereby presenting minimalobstruction at the open top of the container. The particular instancesin which a magnetic stirrer may be found to be of advantage are numerousand include, for example, laboratory type procedures, such as titration,involving the mixing of various chemicals wherein it is important tocontrol the amount of chemical being added, observe the process, andmaintain a uniform distribution of the chemicals within the container.

A magnetic stirrer is generally used in connection with a magneticstirring element disposed within the vessel containing the fluid to bestirred. The magnetic stirrer incorporates a magnet structure providinga magnetic field, and the fluid containing vessel is supported such thatthe stirring element therein is within the magnetic field. The magnetstructure is then rotated or otherwise moved to cause a correspondingmovement of the stirring element and consequent agitation of the fluid.The magnetic stirrer may incorporate a hot plate for maintaining thefluid at a desired temperature, a light or lights for providingillumination of the fluid in the vessel, and means for varying the speedof the magnet structure to provide for different degrees of fluidagitation.

Magnetic stirrers of heretofore known construction have sometimes beensubject to certain limitations. O e major limitation frequentlyencountered in prior art devices has been their inability to accommodatea wide range of magnetic stirring element sizes. Thus, a given sizemagnetic stirrer of prior known construction may only be usable for alimited range of vessel sizes. Previous attempts at designing magneticstirrers to accommodate a wide range of stirring element sizes have beengenerally unsatisfactory in that, for many sizes, when the stirringelements are moved in a manner for peak efficiency, the elements mayslide, drift, or jump out of position in the vessel due to inadequateholding ability of the magnetic field produced by the magnet structurewithin the stirrer.

It is, accordingly, an object of this invention to provide an improvedmagnetic stirrer.

Another object of the invention is to provide a mag- 3,384,353 PatentedMay 21, 1968 "ice netic stirrer capable of utilization in connectionwith a relatively wide range of stirring element sizes.

A further object of the invention is to provide a magnetic stirrercapable of utilization in connection with a wide variety of stirrerelement sizes at their maximum efliciency without sliding, drifting orjumping.

It is another object of the invention to provide 1311 improved magneticstirrer generally of the type described, which is low in cost and ofsimple reliable construction.

Other objects of the invention will become apparent to those skilled inthe art from the following description taken in connection with theaccompanying drawings wherein:

FIGURE 1 is a perspective view of a magnetic stirrer constructed inaccordance with the invention, and having the top broken away toillustrate internal elements, and

illustrating a beaker broken away to show a stirring element therein;

FIGURE 2 is a top view of a portion of an alternative embodiment of theinvention; and

FIGURE 3 is a side view of the elements illustrated in FIGURE 2.

Very generally, the magnetic stirring device 11 of the inventioncomprises a first permanent magnet structure 12 formed of a materialsuch as Alnico and having a pair of first pole portions 13 of oppositepolarity, and a second permanent magnet structure 14 also formed of amaterial such as Alnico and having a pair of second pole portions 16 ofopposite polarity spaced from the first pole portions. The second poleportions are disposed between the first pole portions on a lineextending between the first pole portions. The first and second magnetstructures are positioned with the respective first and second poleportions of like polarity closest to each other. Means 17 are providedfor supporting a fluid containing vessel 18 with a stirring element 19therein within the magnetic field established by the first and secondmagnet structures. Means are provided for moving the first and secondpole portions in a manner to stir the fluid in the vessel.

Referring now in greater detail to the invention, the magnetic stirrer11 is illustrated in FIGURE 1 for use in stirring the fluid 21 in thevessel 18. The vessel illustrated is a conventionally shaped beaker;however, vessels of other shapes and sizes may also be utilized inconnection with the invention.

The stirring element 19 disposed within the vessel 18 may be of anyshape suitable for achieving the desired stirring eflect. The particularshape of the stirring element 11 will depend upon the shape of thevessel and the materials of which the vessel and the stirring elementare comprised. Thus, if the vessel has a curved bottom, a stirringelement of a generally egg shaped form, rather than the elongated rodform illustrated, may be preferable. Moreover, although the stirringelement is comprised of magnetic material, it may be coated with aprotective substance such as glass or Teflon, depending upon the natureof the fluid being stirred. If desired, the stirring element may includea raised portion (not shown) intermediate its ends so that the elementmay more easily spin in the vessel.

The magnetic stirrer 11 includes a housing 23 having the beakersupporting means or table 17 and a control panel 24. The control panelis provided with a speed control 26, a load mode control 27, and apower-on light 28.

viscosity of the fluid being stirred. The speed control is for providingthe desired degree of agitation in the fluid.

The motor 29 is for rotating the pair of magnet structures 12 and 14,described in detail below, and has a drive shaft, not visible. The driveshaft is drivingly connected to a fan 31 for providing a circulation ofcooling air, and to a cylindrical mount 32, the latter also constitutingpart of the means for moving the pole pieces.

The cylindrical mount 32 is drivingly secured to the end of the motordrive shaft and supports the two magnet structures 12 and 14. The magnetstructure 12 includes an elongated bar 33 supporting the pole portions13 at each end thereof. Each of the pole portions 13 comprises agenerally elongated pole piece and the two pole pieces are disposedparallel to each other. The pole pieces are tapered toward the tipsthereof, and the tips of the pole pieces lie in the same plane, a planewhich extends generally parallel with the plane of the supporting table17 and just underneath it. The elongated bar 33 is comprised of asuitable magnetized material so that the pole pieces 13 are of oppositepolarity as indicated in the drawing.

The second magnet structure 14 is provided with the second pole portions16 thereon. The magnet structure 14 comprises a generally U-shapedmagnet with the pole portions 16 disposed at each tip. The magnetstructure 14 is supported on the elongated bar 33, and a non-magnetic(e.g., aluminum) shim or spacer 34 separates the U-shaped magnetstructure 14 from the elongated bar. The elongated bar 33 rests in adiametrical channel or slot provided in the cylindrical mount 32,projecting from each end thereof. The assembly of the two magnetstructures may be held together by any suitable means, but it ispreferable that the bond be accomplished by means of baked and curedepoxy, not illustrated.

The smaller U-shaped magnet structure 14 is oriented so that its poleportions 16 and the pole portions 13 of the magnet structure 12 are allin general alignment. In addition, the two magnet structures arepositioned with their respective pole portions of like polarity closestto each other, as indicated in the drawing.

The result of the foregoing described construction is the production oftwo magnetic fields. The larger field, produced by the magnet structure12, is highly concentrated at the pole portions 13 due to the taperingshape of the pole portions or pieces, and due to the effect of thesmaller magnetic field established by the magnet structure 14. Thissmaller magnetic field forces the flux lines of the larger magneticfield outwardly toward the opposite ends of the magnet structure 12.

The gap between the pole portions 13 and the pole portions 16 isselected to be sufiicient to prevent the larger magnet structure 12 fromexcessively degrading the effect of the small magnet structure 14. Theprecise positioning of the pole portions 13 and the pole portions 16 maybe arrived at empirically, depending upon the range of stirring elementsizes it is desired to accommodate. Thus, for example, where the magnetstructure 12 is 3 inches in the horizontal direction from the outsidesurfaces of the respective pole portions 13, and where the second magnetstructure 14 is centered on the elongated bar 33, being about of an inchbetween outside surfaces and having a centered inch wide gap about of aninch deep, the device is capable of accommodating bar type stirringelements in the length range from about of an inch to slightly over 3inches. Naturally, this geometry can be changed, if necessary toaccommodate other ranges of stirring element sizes. It is preferred thatthe tops of all pole faces or portions be even or coplanar.

In operation, smaller size stirring elements are centered and held bythe smaller magnetic field established by the magnet structure 14.Larger stirring elements may be centered on and are held securely by thehighly concentrated field established at the pole portions 13 of thelarger magnet structure 12. This particular arrangement insures that avariety of stirring element sizes may be securely locked in and held bythe rotating magnet structures.

In assembling the magnetic stirrer illustrated in FIG- URE 1, it ispreferable that a keeper or magnetic shunt (not shown) be placed on thesmaller structure 14 to reduce the effect of its magnetic field and toenable the magnet structures to be positioned more readily with respectto each other. It is preferable that the magnet structures be orientedproperly (i.e., north to north) before bringing them together, and thatthe smaller magnet structure 14 be brought down perpendicularly to thebar 33 and that relative rotation be avoided.

Referring now to FIGURES 2 and 3, an alternative construction for partof the magnetic stirrer of the invention is illustrated. In thealternative structure, a bushing 41 and a drive shaft 40 are used tosupport and drivingly secure the two magnet structures described belowto a drive shaft of the motor. A fan 42 is secured to the bushing 41, asis the large-r magnet structure 43. The larger magnet structure 43consists of an elongated magnet having its ends 44 and 46 turned toextend transversely of its middle portion 47 and parallel with eachother. The ends 44 and 46 are tapered and comprise pole portions orpieces of the magnet structure 43. The polarities are indicated in thedrawing.

The smaller magnet structure 48 consists of a cylindrical or button typemagnet having a slot 49 extending between the opposite poles or poleportions 51 and 52. A shim or spacer 53 is positioned between the magnetstructure 48 and the middle portion 47 of the magnet structure 43. Theshim or spacer 53 is of non-magnetic material. The entire assembly ofthe two magnet structures may be held together as before, that is, by asuitable epoxy, not illustrated.

The construction illustrated in FIGURES 2 and 3 provides a similararrangement of two magnetic fields as is established by the deviceillustrated in FIGURE 1.

It may therefore be seen that the invention provides an improvedmagnetic stirrer of simple, sturdy and economical construction. Themagnetic stirrer of the invention is capable of accommodating a range ofsizes of stirring elements without being subject to sliding, drifting orjumping thereof. The stir-ring elements are securely locked inirrespective of their size, within the size range for which the magneticstirrer is designed.

Various modifications of the invention in addition to those shown anddescribed herein will become apparent to those skilled in the art fromthe foregoing description and accompanying drawings. Such modificaionsare intended to fall within the scope of the appended claims.

What is claimed is:

1. A magnetic stirring device comprising, a first magnet structurehaving a pair of first pole portions of opposite polarity, a secondmagnet structure having a pair of second pole portions of oppositepolarity spaced from said first pole portions, said second pole portionsbeing disposed between said first pole portions on a line extendingbetween said first pole portions, said first and second magnetstructures being positioned with the respective first and second poleportions of like polarity closest to each other, means for supporting afluid containing vessel with a stirring element therein within themagnetic field established by said first and second magnet structures,and means for moving said first and second pole portions in a manner tomove the stirring element.

2. A device according to claim 1 wherein said moving means include arotary support mechanically coupled to said first and second magnetstructures for rotating same.

3. A device according to claim 2 wherein the axis of rotation of saidrotary support is perpendicular to a line extending through said poleportions and is aligned with a space between said second pole portions.

4. A device according to claim 1 wherein said pole portions comprisegenerally elongated mutually parallel pole pieces having their tipslying generally in the same plane.

5. A device according to claim 4 wherein said first pole pieces of saidfirst magnet structure are tapered toward their tips to concentratemagnetic flux thereat.

6. A device according to claim 1 wherein said first magnet structureincludes an elongated bar and a pair of elongated pole pieces extendingperpendicularly thereto, one at each end, wherein said second magnetstructure includes a generally U-shaped magnet supported on saidelongated bar, and wherein a non-magnetic spacer is disposed betweensaid bar and said U-shaped magnet.

7. A device according to claim 1 wherein said first magnet structureincludes an elongated magnet having its ends turned to extendtransversely of its middle portion and parallel with each other, whereinsaid second magnet structure includes a button magnet supported on themiddle portion of said elongated magnet and having a. slot thereinbetween opposite poles, and wherein a nonmagnetic spacer is disposedbetween the middle portion of said elongated magnet and said buttonmagnet.

References Cited UNITED STATES PATENTS 2,655.011 10/1953 Ihle 259-108 X3,138,370 6/1964 Anderson 259108 3,211,433 10/1965 Ohrostowski 2591083,245,665 4/1966 Steel 259108 X ROBERT W. JENKINS, Primary Examiner.

